Many attempts have been made to modify the properties of polyimides or polyimide-containing compositions by incorporating various aromatic moieties in their molecular structure to provide improved processing characteristics and thermal stability. These polymers, however, have generally not been completely satisfactory in that they do not readily lend themselves to preparation or processing by hot melt procedures, are deficient in thermal stability or may lack other useful characteristics such as good adhesion or solvent resistance.
The preparation of polyimides which are stable at high temperatures is known. Thermally stable polyimides have been prepared by reacting various aromatic tetracarboxylic acids or their derivatives, such as dianhydrides, with aromatic diprimary amines to form polyamide-acids which are soluble in dipolar aprotic organic solvents. The polyamide-acids are then cyclized either by heat treatment or by chemical means to form the polyimides. Such polyimides, however, generally are intractable and infusible as well as being insoluble in most solvents making them difficult, if not impossible, to fabricate into molded parts. Moreover, when a polyamide-acid prepolymer solution is prepared and then heat cured in situ to the polyimide, the temperature required may be too high for the substrate coated and appreciable amounts of water are uncontrollably released in addition to evaporation of the solvent. This raises other limitations as to the type of uses for such materials.
In recent years, various aromatic and heterocyclic materials have been investigated in attempts to obtain thermally stable polyimides that could be more readily prepared and fabricated. It is disclosed, for example, in U.S. Pat. Nos. 3,699,075 and 3,812,159 to Lubowitz, U.S. Pat. No. 3,847,867 to Heath et al and U.S. Pat. No. 3,879,428 to Heath that aromatic diether polycarboxylic acids and anhydrides thereof could be reacted with aromatic diamines to prepare thermally stable, high molecular weight polyimides which are soluble in organic solvents and fusible. Such polyimides are suggested as being suitable for use in preparing coatings, adhesives, films and the like or for fabrication into useful parts by conventional molding equipment. However, known polyimides prepared in this manner appear to exhibit certain deficiencies such as low Tg, inadequate adhesion to many substrates, and generally poor solvent resistance.
It has also been suggested, for example, in U.S. Pat. Nos. 4,017,459; 4,064,289; 4,239,880; and 4,405,770 that aromatic diether diamines can be reacted with tetracarboxylic acid and its derivative to prepare soluble poly(amide-imides) or polyimides which may also be melt processible. Further, in U.S. Pat. No. 3,563,951 it is suggested that thermally stable polyimides which are fusible and soluble can be prepared by reacting high molecular weight diamine capped aromatic polyether oligomers with non-diether containing aromatic tetracarboxylic acid or an anhydride derivative thereof. The uncertainty of being able to prepare soluble and melt processible polyimide and poly(amide-imide) polymers from such aromatic diamines is shown by other researchers where, for example, in a paper by George L. Brode et al., published in Journal of Polymer Science, Vol. 12, pp. 575-587 (1974) it is reported that polymers prepared with aromatic diether diamines containing a sulfonyl linkage were more melt processible than polymers having a propane linkage and in a paper published in Makomolecular Science, Vol. 1, pp. 667-670 (1980) it is reported that the reaction of 2, 2-bis[4-(p-aminophenoxy)phenyl]propane with pyromellitic dianhydride and 4,4'-carbonyldi(phthalic anhydride) resulted in the preparation of insoluble polyimides.